Volatile organic chemicals are commonly released to the environment as non-aqueous phase liquids(NAPL) via surface spillage, storage tank leakage, or leaching from hazardous waste landfills. The presence and behavior of NAPL in subsurface systems has not been adequately accounted for in prior aquifer modeling efforts. This is one of two companion projects to be conducted at the University of Michigan to address that deficiency. This project will focus specifically on the mass transfer of chemicals from organic liquid phases to aqueous and vapor phases. Experiments will be conducted to examine VOC mass transfer from immiscible organic liquids at residual saturation in packed columns of porous media. Liquid-liquid and liquid-vapor interphase transfer processes will be described in terms of appropriate mass transfer coefficients and driving forces. Correlations between the characteristics of the porous media (e.g., grain size distribution) and the mass transfer coefficient will be established. Variations in flow rate, configuration of the immiscible phase, initial wetting fluid, and column length will permit quantification of rates of mass transfer. A generalized mathematical model describing the kinetics of mass transfer and transport through the porous media will be written to aid in the analysis of the data obtained from these experiments. The model will include a mass balance for the non-aqueous liquid phase. Local equilibrium partitioning and kinetic mass transfer expressions will be incorporated as options in the model to describe the interphase mass exchange. Departures from local equilibrium will be modeled using several phenomenological mass transfer expressions related to the properties of the immiscible phase and the porous media. Based on this analysis, that specifically configured mass transfer model which most closely characterizes the observed data will be identified and incorporated as a "sub-model" in the computer simulator being developed in the companion project.